Kathmandu, May 3 (IANS): Nepal has imposed restrictions on heavy aircraft transporting humanitarian aid to Nepal to prevent further damage to the five-decade-old runway at the Tribhuvan International Airport here.

The decision means that planes weighing more than 196 tonnes will not be permitted to land.

A senior government official told IANS that some Western countries have sought permission to land big jets carrying relief materials following the April 25 killer earthquake.

However, the restrictions do not apply to scheduled international flights, whatever the type of the aircraft.

Airport sources said the US had planned to bring in relief materials on a Boeing 747.

Airport officials said the decision was taken after three cracks appeared on the runway.

More than 300 rescue flights, including 150 chartered ones, have landed here since a powerful earthquake rattled Nepal on April 25 leaving thousands dead.

"As the runway problem has started to reappear, we cannot afford to permit landing of heavy jets," said a senior official. "Unless we act now, our only international airport could be at risk of closure."

This is the second time in two years that the airport has imposed such restriction due to cracks on the runway.

In August 2013, the airport authority asked all international carriers to find alternatives to wide-body aircraft flying into the airport.

The cracks first appeared on the runway in June 2011 and have become a recurring problem.